Lab 6 Resistance Combinations

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San Jacinto Community College *

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Electrical Engineering

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Apr 3, 2024

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012-05892C AC/DC Electronics Laboratory 1 ® EQUIPMENT NEEDED: – AC/DC Electronics Lab Board: Resistors – Multimeter Purpose The purpose of this lab is to begin experimenting with the variables that contribute to the opera- tion of an electrical circuit. This is the first of a three connected labs. Procedure ➀ Choose three resistors of the same value. Enter those sets of colors in Table 4.1 below. We will refer to one as #1, another as #2 and the third as #3. ➁ Determine the coded value of your resistors. Enter the value in the column labeled “Coded Resistance” in Table 4.1. Enter the Tolerance value as indicated by the color of the fourth band under “Tolerance.” ➂ Use the Multimeter to measure the resistance of each of your three resistors. Enter these values in Table 4.1. ➃ Determine the percentage experimental error of each resistance value and enter it in the appropri- ate column. Experimental Error = [(|Measured - Coded|) / Coded ] x 100%. Table 4.1 Colors 1st 2nd 3rd 4th Coded Resistanc e Measured Resistanc e % Error Tolerance #1 Orange, Orange, Brown, Gold 330 326 1.22  5% #2 Orange, Orange, Brown, Gold 330 323 2.14  5% #3 Orange, Orange, Brown, Gold 330 326 1.22  5% ➄ Now connect the three resistors into the SERIES CIRCUIT, figure 4.1, using the spring clips on the Circuits Experiment Board to hold the leads of the resistors together without bending them. Measure the resistances of the combinations as indicated on the diagram by connecting the leads of the Multimeter between the points at the ends of the arrows. Experiment 4:Resistances in Circuits

R 2 R 1 R= 1 R 3 R= 166 ohms 23 R= 490 ohms R R 12 3 123 123 R AC/DC Electronics Laboratory 012-05892C 2 ® Series Figure 4.1 ➅ Construct a PARALLEL CIRCUIT, first using combinations of two of the resistors, and then using all three. Measure and record your values for these circuits. Parallel ➆ Connect the COMBINATION CIRCUIT below and measure the various combinations of resistance. Do these follow the rules as you discovered them before? It does seem to follow the same rules. Combination Figure 4.2 327 ohms Figure 4.3 ⑧ Choose three resistors having different values. Repeat steps 1 through 7 as above, recording your data in the spaces on the next page. Note we have called these resistors A, B and C. R 1 R 2 R 3 R = 651 ohms 12 R 12 ➤ R = 650 ohms 23 R 23 ➤ R = 977 ohms 123 R 123 ➤ R 1 R R = 164 ohms 12 12 R = 23 165 ohms R 2 R= 123 110 ohms R 3 ➤ ➤ ➤ ➤ NOTE: Include also R by 13 replacing R with R . 2 3 ➤ ➤ ➤ ➤ ➤ ➤ ➤

012-05892C AC/DC Electronics Laboratory 3 ® Discussion ➀ How does the % error compare to the coded tolerance for your resistors? The percent error does seem to be within the coded tolerance. ➁ What is the apparent rule for combining equal resistances in series circuits? In parallel circuits? Cite evidence from your data to support your conclusions. As resistances are combined in series, the resistance seems to be multiplied by the number of resistors. Looking at figure 4.1, the resistances match this, with some variations. As 330 *2 is 660, the resistances in figure 4.1 that are only looking at two resistors combined are close to this value. As resistances are combined in parallel, the resistance seems to decrease. The resistance seems to be divided by the number of resistors there are. This is seen in Figure 4.2. ➂ What is the apparent rule for combining unequal resistances in series circuits? In parallel circuits? Cite evidence from your data to support your conclusions. In series, this adds the resistance together to find the total resistance. This can be seen in figure 4.1, as the resistances can be added to get those values. In parallel, the resistances follow 1/R(total) = 1/R(1) + 1/R(2) + … for as many resistors in the same parallel connection. This could be seen in figure 2, as it follows this. ➃ What is the apparent rule for the total resistance when resistors are added up in series? In parallel? Cite evidence from your data to support your conclusions. The rule for series is to add up all the resistance values. R T =R 1 +R 2 +R 3 +… The rule for parallel is to add up all the resistance’s inverse. 1/ R T =1/R 1 +1/R 2 +1/R 3 +… Reference Figure 4.7 Black Brown Red Orang e Yello w Green Blue Violet Gray White 0 1 2 3 4 5 6 7 8 9 2nd Digit 1st Digit No. of Zeros Tolerance Fourth Band None  20% Silver  10% Gold  5% Red  2%

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